WIDE-RANGE PRECISION CONSTANT VOLUME GAS THERMOMETER

摘要

A Constant Volume Gas Thermometer (CVTG) device for measuring the temperature with high precision over a wide temperature range comprises a pressure measurement device, which comprises a mechanical assembly forming a membrane. The capillary tube communicates with the bottom side of the membrane and a first pressure measurement element on the membrane generates a signal in dependence of a deformation of the membrane. Further, the CVTG comprises electronic means for reading and correlating the signal of said first pressure measurement element to the temperature of the gas cartridge. The gas volume inside the pressure measurement device is minimized by careful design and tight tolerances. To measure pressures below 0.1 MPa inside the CVGT with sufficient accuracy, the CVGT include a second pressure measurement device which is based on the Pirani measurement principle. A Pirani measurement device measures the thermal conductivity of the surrounding gas. To this end, a thermally insulated wire or surface is heated electrically to a defined temperature, while the surrounding gas is at ambient temperature. If the thermal conductivity of the surrounding gas changes, either the Pirani element's temperature changes, or the electrical heating power needs to be adapted in order to maintain the Pirani element's temperature.